1. Field of the Invention
The present invention relates to optoelectronic apparatus, for example to signal interconnects between the electronics and the optical transmission medium and vice versa.
Advanced systems for long distance and short distance communication need very high speed interconnects for the inter system as well as intra system information transmission. The standard technology for this purpose is optical transmission over fibres. The key components for the aforementioned technology include the electro-optic (e-o) transducer acting as a transmitter, and the opto-electronic (o-e) transducer acting as a receiver. Such transducers are used in every optical communication system.
For the very high transmission speeds of 10 Gigabites per second (10 Gbit/sec) and above it is necessary to apply high speed optical and electronic components as well as special solutions for the packaging of such a transducer module in order to reach the required overall high-frequency (HF) performance.
A further increase of the transmission capacity is possible with parallel transmission of several channels. In this case there are additional critical issues that must be solved because a close spacing of radio frequency (RF) channels may lead to crosstalk and signal degradation. Therefore the proper design of the electronics and the packaging is even more challenging.
A transmitter or receiver module in general consists of the module housing with an electronic interface and an optical interface and the opto-electronic assembly inside the housing. The opto-electronic assembly consists of an arrangement of: 1) optical components such as laser diode and photodiode chips; 2) active electronic components such as patterned circuit boards and mounted integrated circuits; and 3) other mechanical or passive optical components, wherein all components are placed inside the housing. For parallel transmission there are typical several parallel channels and components on each optical or electronic chip. This configuration has the advantage that it is possible to reach higher density and lower cost.
To achieve good HF-performance with such an opto-electronic assembly it is necessary to use a circuit board with impedance-matched electrical transmission lines as well as an assembly and interconnection technology that is optimized for high speed signal transmission. Furthermore, the opto-electronic assembly has to comply with the type and performance specifications of the applied optical and electronic components.
Such opto-electronic assemblies are used inside packages that include an optical and an electronic interface (or port) which may have several independent parallel channels each. The optical interface of such a package is attached to an optical connector or optical fibre port and forms what is called a subassembly. The subassemblies with an optical connector for departing or entering optical data signals are called transmitter optical subassemblies (TOSAs) and receiver optical subassemblies (ROSAs), respectively. Such subassemblies are used as building blocks in higher complexity integrated modules such as various types of transceivers or transponders that include a TOSA and a ROSA and also various kinds of electronic functions via an electronic port. For these types of applications there is only a limited physical space and it is necessary that the package is designed in a geometry wherein the optical port and the electronic port are located on opposite sides of the package. Further such subassemblies may contain optical transmitting channels as well as optical receiving channels. Sometimes these subassemblies are called “optical engines”.
2. Description of Related Art
Prior art of parallel optical assemblies for high speed interconnections with top-emitting transmitters like Vertical Cavity Surface Emitting Lasers (VCSELs) apply an optical polymer component for beam forming which is arranged at some distance on top of the transmitter chip. The polymer component includes a micro-lens, a mirror section and a further micro-lens for each optical channel located in front of each laser (see FIG. 1). A new version of such an optical polymer component is presented in the US patent application entitled “Lens Array and Optical Module Including Lens Array” by Morioka, filed Jul. 6, 2011, patent application Ser. No. 13/177,307, whereas this patent application is hereby incorporated by reference.
Another approach is published as “Parallel optical link (PAROLI) for multichannel gigabit rate interconnections”, H. Karstensen et. al., ECTC Conference, pp. 747-754, 1998, whereas this publication is incorporated herein by reference. On top of the transducer chip with several VCSELs an optical fiber is aligned, having the endface polished in a 45° angle. This angled surface is used as a mirror to direct the emitted laser light from the VCSEL into the fiber which is arranged parallel to the surface of the transducer.